The present invention is directed to a device and method for determining the surface configuration of a log in a charger of the type which supplies logs to a veneer lathe. The device and method of the present invention provide for orienting the log such that an optimum longitudinal axis of the log is aligned with the lathe spindles of the veneer lathe when the log is supplied to the lathe. More particularly, the present invention is directed to such a device and method which utilize ultrasonic scanning of the log.
In processing logs into veneer, standard length logs, termed peeler blocks, are received by a charger device associated with the veneer lathe. The charger then loads the log into the lathe where it is peeled into a strip of veneer. In a number of prior art charger systems, alignment of the block is accomplished under control of an operator and, as a result, substantial errors may be made by the operator in locating the optimum spin axis for rotation of the block in the lathe. Since the size and surface contour of logs varies substantially, it is not possible for an operator to determine consistently and accurately the optimum spin axis, especially since logs must be loaded into the veneer lathe in succession at a relatively high rate.
In order to increase the accuracy with which logs are positioned in a veneer lathe, a number of charger systems have been devised which provide for approximate mechanical centering of a log in the log charger, prior to loading the log into the lathe. In one such system manufactured by Durand Machine Co., Ltd., New West Minster, British Columbia, Canada, the log is supplied to a set works consisting of a pair of vertically movable members defining V-shaped surfaces which cradle the log. The log is then raised by the set works while, simultaneously, feeler arms are lowered. When the arms contact the top of the log, movement of the set works is terminated and the log is assumed to be substantially aligned with a fixed axis of the charger. A pair of carrying arms then engage opposite ends of the log and carry the log into position in the veneer lathe.
In another mechanical charger arrangement, manufactured by Coe Manufacturing Company, Painesville, Ohio, a pair of support arms are provided, each arm having three log engaging members mounted thereon which press against three sides of the log. By means of a mechanical linkage arrangement interconnecting the members, the members move the log into a position substantially aligned with a fixed axis of the charger. Thereafter, the support arms are pivoted and carry the log into position in the veneer lathe. At best, the Durand and Coe charger systems only approximately center the logs, since these systems do not take into account any variations in the logs which exist between the points at which the logs are mechanically engaged.
A number of veneer lathe charger systems have been developed in which the contour of the surface of a log and the radius or diameter of the log at a number of points along its length are monitored in order to determine the optimum alignment of the log with respect to the veneer lathe rotational axis. Generally, such systems have utilized photo-optical scanning of a log to determine its shape and surface contour. U.S. Pat. No. 3,852,579, issued Dec. 3, 1974, to Sohn et al. and U.S. Pat. No. 3,992,615, issued Nov. 16, 1976, to Bennett et al., disclose electro-optical ranging systems in which light directed from a light source to strike the log surface is reflected from the surface to a photo-electric detector. The light from the light source is modulated in such a manner that the distance from the source and detector to log surface may be measured. The log is rotated during this optical scanning operation. By subtracting the measured distance from the light source and detector to the log surface from the known distance between the light source and detector and the axis of rotation of the log, the radii of the log at a number of angularly spaced positions around the log periphery are determined. This information is then utilized by a computer to determine the optimum rotational axis for the log in the veneer lathe.
In U.S. Pat. No. 3,902,539, issued Sept. 2, 1975, to Ketteler, a device is disclosed for centering the longitudinal axis of a log in which two set works members defining V-shaped log cradling surfaces are raised until the upper surface of the log breaks several beams of light. The beams extend tangentially with respect to the upper surface of the log in an inverted V-shape. The set works may be adjusted, both vertically and horizontally to center the log with respect to a fixed axis.
Finally, U.S. Pat. No. 4,197,888, issued Apr. 15, 1980, to McGee et al., discloses a log centering device, generally of the type described above with respect to the mechanical centering charger manufactured by Coe Manufacturing Company. The disclosed log centering device, however, includes a plurality of light sources which project tangential beams of light adjacent the periphery of the log as the log is rotated on a spindle arrangement in the charger, subsequent to an approximate mechanical centering operation. The log is then regripped by the log engaging members on the support arms and its position is adjusted by movement of the members. Finally, a separate pair of arms engage opposite ends of the log and pivot the log into position in the veneer lathe.
It will be appreciated that the above described prior art devices are not suitable for retrofitting onto existing chargers of the type which geometrically center logs in mechanical operation. A number of the above described devices require an additional spindle arrangement in the charger for rotating the logs during the scanning operation. Also, the charging process is slowed by the need to rotate the logs in the charger during scanning. Finally, photo-optical scanning, utilizing one or more beams of light which are directed tangentially with respect to a log, does not provide a completely accurate representation of variations in the log radius.
It is seen, therefore, that there is a need for a simple, accurate device for orienting a log in a veneer lathe charger, prior to loading the log into the lathe, in which accurate measurements of the variations in the log surface may be made and which is suitable for retrofitting on existing veneer lathe chargers.